The DNA polymerase from Thermophyllus aquaticus (Taq) is a thermostable enzyme extensively used to generate DNA fragments by the polymerase chain reaction (PCR). Our goal is to study the structural basis for thermostability of this polymerase. An explanation for thermostability may only be obtained by determining the 3-D structure of the enzyme. The aim of the current investigation is to study crystallographically the KlenTaq DNA polymerase and its complexes with DNA.